Postemergence Winter Weed Control in Bermudagrass (Cynodon dactylon) Turf

Abstract

Several herbicides were applied in January, February, and March with a comparison of the intervals of treatment of 2 and 4 weeks after the initial treatment each month for postemergence control of winter annual weeds in bermudagrass [Cynodon dactylon (L.) Pers.] turf. Glyphosphate [N-(phosphonomethyl)glycine] treatments applied at 2-week intervals with the initial treatment made in January or February controlled a higher percentage of annual bluegrass (Poa annua L.) than when applied in March. Hop clover (Trifolium agrarium L.) control was also higher when glyphosate was initially applied in January or February than when applied in March regardless of time interval between first and second treatment. Combination treatments of (a) 2,4-D [(2,4-dichlorophenoxy)acetic acid] + dicamba (3,6-dichloro-o-anisic acid) and (b) 2,4-D + mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} + dicamba applied at 2-week intervals with the initial treatment made in January or February controlled more corn speedwell (Veronica arvensis L.) and hop clover than when applied in March. Highest henbit (Lamium amplexicaule L.) control was obtained from the combination 2,4-D treatments made at 4-week intervals when initial treatment was made in February and March. Weed control was not influenced by dates and interval of repeated treatments with either paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] treatments. Germination and regrowth of weeds were greater in plots treated with glyphosate and paraquat initially in January or February than other herbicide-treated plots. Weeds were not reestablished in any of the atrazine-treated plots. Paraquat and combinations of 2,4-D + dicamba or 2,4-D + mecoprop + dicamba injured bermudagrass when applied initially in January and February even though they were applied to turf that appeared dormant. All herbicides injured bermudagrass more when applied to semi-dormant turf in March than to dormant turf in January or February. Atrazine affected bermudagrass less than any of the other herbicides tested when initial treatment was applied in March to semi-dormant turf.